The present invention relates to a scattering light smoke alarm.
It is known to utilize scattering light smoke alarms. In the known scattering light smoke alarms the scattering point of a light emitter and a light receiver is located outside the scattering light smoke alarm. This has the advantage that no measuring chamber with a labyrinth must be provided. Smoke alarms with a labyrinth have the disadvantage that the labyrinth can be clogged with dirt. It is believed that such scattering light smoke alarms can be further improved.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a scattering light smoke alarm, in which the scattered light smoke alarm has a cover for protection of a light transmitter and a light receiver, and means for distinguishing between smoke and other foreign bodies, which is located in a region around the scattering point.
When the scattering light smoke alarm is designed in accordance with the present invention it has the advantage that a distinguishing between permanent foreign bodies in the scattering point of the scattered light smoke alarm and actual smoke is possible.
Such foreign bodies can be for example conductors which are cut off for manual works, or boxes which are stacked over one another. Also, spiders can make their nets in narrow shafts in the free space of the scattered light smoke alarm and by accident be located in the scattering point of the scattering light smoke alarm. The inventive scattering light smoke alarm recognizes such foreign bodies and eliminates them from the measuring signals, so that false alarm messages can be avoided.
In accordance with the present invention the means for distinguishing between smoke and other foreign bodies can include a processor for analysis of the time course of receiving signals of the light receiver, and the processor can be connected to the light receiver. With the time course it is advantageously possible to determine whether smoke or another foreign body is located in the scattering light smoke alarm. With smoke an increasing intensity of the scattering light signal is registered with increasing time, while when a foreign body penetrates in the scattering point a jump function occurs over a short time, and then again is drawn in a fixed signal. This distinguishing with respect to a jump in the time function makes possible the distinguishing in a simple manner between smoke and another foreign body. Therefore there is also an advantage that an available scattering light smoke alarm must be just completed with a software, which performs this time analysis of the receiving signal of the light receiver. Thereby the inventive scattering light smoke alarm can be realized in a simple manner.
In accordance with another embodiment of the present invention, it is advantageous when an optical element, preferably a facet mirror is arranged around the light receiver, to couple the scattering signals in the light receiver from a region area around the scattering point. The total signal at the light receiver is an integral of the signals from all scattering regions in this area. With a suitable facet mirror it is possible to detect many scattering regions which are located spatially apart from one another, in which the alarm sensibly reacts to scattering light. When smoke is present, then all scattering regions homogeneously with the corresponding smoke density supply a portion of a scattering light signal, while a spider locally scatters a partial signal at the receiver. With such an arrangement, by simple amplitude comparison, a spider can be distinguished from smoke.
In a further advantageous embodiment of the scattering light smoke alarm of the present invention, is formed so that the distinguishing between smoke and another foreign body is made possible in that the light source is formed with adjustable wave lengths. Thereby advantageously the effect is utilized that with the Rayleigh scattering, the scattering condition is independent from the wavelength of the radiation. With the use of a variable frequency laser, in presence of smoke particles, different signal intensities as a function of the wavelength are obtained for the Rayleigh scattering. For particles which are large relative to the wavelength, the scattering does not depend or depends only insignificantly from the wavelength, and therefore with a variable frequency of the light transmitter no significant effect with the scattering signals occurs. With small particles such as smoke particles, this effect of the intensity variation in dependence on the wavelengths is significantly measurable. Thereby it is advantageously possible to distinguish such smoke particles from larger particles. This distinguishing is then performed by a processor in the inventive scattering light smoke alarm.
A further advantage resides in that the light transmitter can be connected with an amplitude modulator. Amplitude-modulated light signals make possible on the one hand due to the phase shift between transmitted and received signals which are the pulses which are produced from the amplitude modulation, a distance determination of the scattering object, while a pulse widening or in other words a dispersion is measured for a diffusing scattering body which is first of all a smoke cloud. Thereby in advantageous manner it is possible that, in dependence on the pulse widening, it can be determined whether smoke or another foreign body is present.
Finally, in accordance with another embodiment of the present invention it is advantageous that the scattering light smoke alarm has an ultrasound sensor which contains a transmitter and a receiver. The ultrasound sensor can be arranged so that the ultrasound sensor monitors the area around the scattering point. The ultrasound sensor monitors thereby advantageously the optical scattering region of the scattering alarm. If a solid foreign body is located in the scattering region, the ultrasound sensor and the scattering light sensor receive a signal. If smoke is located in the scattering point, only the scattering light sensor receives a signal, but not the ultrasound sensor. For this purpose ultrasound sensors with operating megahertz region are suitable, since these ultrasound sensors have a very good directional action. By means of the ultrasound sensor it is further advantageously determined whether a foreign body is located in a region around the smoke alarm, which possibly indicates an influence of the current condition for the fire detection. This can be outputted as a warning for the central unit.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.